The present invention relates to a drive unit which includes a vibrator with a piezoelectric body.
Conventionally, an ultrasonic actuator is known as a driving device which includes a piezoelectric element (electromechanical conversion element) for use in various electric devices and other types of devices (e.g., Patent Document 1).
An ultrasonic motor drive unit described in Patent Document 1 at least includes an ultrasonic vibrator which excites the first vibration mode and the second vibration mode, a slider plate actuated by this ultrasonic vibrator, a pressing member which presses the ultrasonic vibrator against the slider plate, and power supply means for applying an alternating voltage to an electromechanical converter included in the ultrasonic vibrator. In the state where the ultrasonic vibrator is pressed against the slider plate with a predetermined force, the resonance frequency of the first vibration mode in which vibration occurs in a direction perpendicular to the direction of movement of the slider plate is lower than the resonance frequency of the second vibration mode in which vibration occurs in the direction of movement of the slider plate. The ultrasonic vibrator is actuated at a frequency between the resonance frequency of the first vibration mode and the resonance frequency of the second vibration mode.    Patent Document 1: Japanese Laid-Open Patent Publication No. 9-224385